Lubricant composition comprising a 2,5-dimercapto-1,3,4-thiadiazole alkyl polycarboxylate compound

ABSTRACT

A lubricating oil additive composition comprising at least one organomolybdenum compound and at least one 2,5-dimercapto-1,3,4-thiadiazole alkyl polycarboxylate compound.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. National Phase Application under 35 U.S.C. § 371 of International Patent Application No. PCT/EP2021/058073 filed Mar. 29, 2021, which claims priority of French Patent Application No. 20 03253 filed Apr. 1, 2020. The entire contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to the field of lubricant compositions, in particular to the fuel economy (FE or “fuel eco”) properties of lubricant compositions. More specifically, the invention concerns an additive composition which makes it possible to maintain the fuel economy properties of a lubricant composition (FE retention or “fuel eco retention”) over time. The invention also relates to the use in a lubricant composition of an additive composition according to the invention as well as the resulting lubricant composition.

BACKGROUND

Engine development and the performance of engine lubricant compositions are inextricably linked. The more complex the engine design, the higher the efficiency and fuel consumption optimization and the more the performance of the lubricant composition must be improved.

The operating conditions for gasoline and diesel engines include both extremely short and long journeys. Indeed, 80% of car journeys in Western Europe are less than 12 kilometers, while some vehicles cover annual distances of up to 300,000 km.

Oil change intervals also vary widely, from 5,000 km for some small diesel engines to up to 100,000 km for modern commercial diesel engines.

Lubricant compositions for motor vehicles must be adaptable to all these conditions of use and thus must have improved properties and performance.

Engine lubricant compositions have to fulfil many objectives.

The lubrication of parts that slide on each other plays a key role, particularly in reducing friction between these parts and thus wear and tear, which in turn saves fuel.

An essential requirement of engine lubricant compositions is the environmental aspects. It has become essential to reduce fuel consumption in order to reduce CO₂ emissions.

The nature of automotive engine lubricant compositions has an influence on fuel consumption. Fuel-saving automotive engine lubricant compositions are often referred to as “fuel eco” (FE).

Improving the level of fuel eco performance is constantly sought in the formulation of automotive lubricants.

However, this improvement in performance is not enough. It must be accompanied by the maintenance or preservation over time of this level of fuel eco performance obtained through the use of the lubricant compositions.

When using a lubricant composition in an engine that causes the engine to age, the fuel eco performance should be maintained as much as possible. Indeed, a decrease in fuel eco performance reduces the benefits. Thus, in addition to the need to achieve a high level of fuel eco performance, it is important to be able to maintain or preserve this level of fuel eco performance of a lubricant composition over time, for example between two oil change intervals or after a certain number of kilometers have been driven.

In particular, it is important to have lubricant compositions that maintain good fuel economy of an engine, especially a vehicle engine.

Friction modifiers such as organomolybdenum compounds are known to be added to lubricant compositions to lower the coefficient of friction. The addition of such compounds results in fuel savings and gives the lubricant FE properties. Among the friction modifiers used, MoDTC (molybdenum dithiocarbamate) is one of the most effective additives for lowering the coefficient of friction and thus achieving fuel savings.

During engine operation, the organomolybdenum compound such as MoDTC forms two compounds, MoS₂ (lamellar molybdenum disulphide), which reduces friction, and molybdenum trioxide (MoO₃) which tends to increase wear.

The Molybdenum forming part of the organomolybdenum compound oxidizes which is responsible for the loss of performance of the organomolybdenum compound over time and therefore a loss of performance of the Fuel Eco lubricant composition (and therefore fuel economy) over time.

To overcome this problem, organic friction modifiers can be used, but they are less effective. An increase in the amount of organomolybdenum compound was also considered. A high molybdenum content, however, represents a considerable additional formulation cost. On the other hand, at high levels, typically above 1,500 ppm, the lubricant compositions are no longer stable, and these stability problems result in a high risk of engine fouling and/or engine corrosion, especially in copper engines.

There is therefore a need for engine lubricant compositions, especially for vehicle engines, which can solve some or all of the problems of the lubricant compositions of the prior art.

SUMMARY

It is an objective of the present invention to provide a lubricant composition with prolonged fuel economy properties over time and thereby maintain a reduction in fuel consumption over time.

A further objective of the present invention is to provide a lubricant composition that maintains a low coefficient of friction over time.

A further objective of the present invention is to provide a solution to the decrease in efficiency of the organomolybdenum compound over time.

A further objective of the present invention is to provide a compound that protects the organomolybdenum compound of a lubricant composition from degradation over time, particularly by oxidation.

Further objectives will become apparent from the following description of the invention.

The invention relates firstly to a lubricating oil additive composition comprising:

-   -   at least one organomolybdenum compound, and     -   at least one 2,5-dimercapto-1,3,4-thiadiazole alkyl         (poly)carboxylate compound.

The invention also relates to a lubricant composition comprising:

-   -   at least one base oil, and     -   at least one additive composition as defined above and detailed         below.

The invention finally relates to the use of a 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound in a lubricant composition comprising at least one base oil and at least one organomolybdenum compound, preferably chosen from dinuclear organomolybdenum compounds.

Preferably, the 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound is used to maintain the fuel economy of an internal combustion engine over time.

Advantageously, the mass ratio between the organomolybdenum compound and the 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound ranges from 1:100 to 100:1, preferably from 1:10 to 10:1, more preferably from 1:5 to 5:1.

Advantageously, the organomolybdenum compound is chosen from dinuclear organomolybdenum compounds, preferably from molybdenum dithiocarbamates.

Advantageously, the 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound is selected from compounds of the following formula (IV):

wherein R′ is a C₁-C₃₄ alkyl moiety substituted with at least one C₁-C₃₄ alkyl carboxylate moiety, preferably at least two C₁-C₃₄ alkyl carboxylate moieties. Preferably, the moiety R′ is a C₁-C₃₀, preferably C₁-C₂₀, more preferably C₁-C₁₀, typically a C₁-C₅ alkyl moiety, for example is an ethyl moiety.

Preferably, the alkyl carboxylate moiety(-ies) are independently selected from C₁-C₃₀, preferably C₁-C₂₀, more preferably C₁-C₁₀, alkyl carboxylate moieties, for example is a 2-ethylhexyl moiety.

More advantageously, the 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound has the following formula (V):

Preferably, the lubricant composition comprises from 50% to 99.5% by weight of base oil(s) relative to the total weight of the lubricant composition.

Preferably, the content of the element molybdenum in the lubricant composition ranges from 50 to 1,500 ppm by weight, preferably from 100 to 1,000 ppm by weight, compared to the total weight of the lubricant composition.

Preferably, the lubricant composition comprises from 0.2% to 1.0% by weight of 2,5-dimercapto-1,3,4-thiadiazole, alkyl (poly)carboxylate compound, preferably from 0.2% to 0.9% by weight, e.g. 0.5% by weight, compared to the total weight of the lubricant composition.

Advantageously, the lubricant composition has a sulphur content ranging from 0.01% to 5% by weight, preferably from 0.1% to 2% by weight, more preferably from 0.1% to 0.5% by weight, compared to the total weight of the composition.

Without being bound by any theory, the 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound is more thermally stable than other sulphur compounds used in lubricant compositions such as a polysulphide compound or a phospho-sulphur compound. Thus, the presence of the compound 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate in a lubricant composition comprising an organomolybdenum compound, such as molybdenum dithiocarbamate, also called MoDTC, enables the oxidation of molybdenum to be reduced or even protected from oxidation and promotes the sulphurisation of the organomolybdenum compound and the sulphurised by-products of molybdenum and thus maintains the properties of the organomolybdenum compound, such as MoDTC, over time.

Without being bound by any theory, the combination of a 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound with an organomolybdenum compound, such as MoDTC, allows for the maintenance of a low coefficient of friction over time, the maintenance of the FE properties of the lubricant over time, and thus fuel economy over time.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows the evolution of the coefficient of friction of a composition according to the invention and a reference composition as a function of the engine operating time.

DETAILED DESCRIPTION

The invention relates to a lubricating oil additive composition comprising:

-   -   at least one organomolybdenum compound, and     -   at least one 2,5-dimercapto-1,3,4-thiadiazole alkyl         (poly)carboxylate compound.

The invention also relates to a lubricant composition comprising:

-   -   at least one base oil,     -   at least one organomolybdenum compound, and     -   at least one 2,5-dimercapto-1,3,4-thiadiazole alkyl         (poly)carboxylate compound.

An organomolybdenum compound according to the invention means any fat-soluble organomolybdenum compound.

The organomolybdenum compound according to the present invention may be selected from organic molybdenum complexes comprising at least one chemical element molybdenum (Mo), preferably at least two chemical elements molybdenum (Mo), and at least one ligand such as a carboxylate ligand, an ester ligand, an amide ligand, a dithiophosphate ligand, a dithiocarbamate ligand.

For example, organic complexes of molybdenum with carboxylates, esters and amides can be obtained by reacting molybdenum oxide or ammonium molybdates with fats, glycerides, fatty acids or fatty acid derivatives (esters, amines, amides, etc.).

For the purposes of the invention, carboxylate ligands, ester ligands and amide ligands are free of sulphur and phosphorus.

In one embodiment, the organomolybdenum compound of the invention is selected from complexes of molybdenum with amide ligands, mainly prepared by reacting a source of molybdenum, which can be for example molybdenum trioxide, and an amine derivative, and fatty acids comprising for example from 4 to 36 carbon atoms such as for example fatty acids contained in vegetable or animal oils.

The synthesis of such compounds is for example described in U.S. Pat. No. 4,889,647, EP0546357, U.S. Pat. No. 5,412,130 or EP1770153.

In a preferred embodiment, the organomolybdenum compound is selected from dinuclear organomolybdenum compounds.

For the purposes of the invention, “dinuclear organomolybdenum compound” means organomolybdenum compounds with two molybdenum atoms in the nucleus. They are also known as dimeric organomolydbene compounds.

In a preferred embodiment of the invention, the organomolybdenum compound is selected from organic complexes of molybdenum with amide ligands obtained by the reaction of:

(i) a mono-, di- or tri-glyceride fat or fatty acid,

(ii) an amino source of formula (A):

In which:

-   -   X¹ represents an oxygen atom or a nitrogen atom,     -   X² represents an oxygen atom or a nitrogen atom,     -   n or m represents 1 when X¹ or X² respectively represents an         oxygen atom,     -   n or m represents 2 when X¹ or X² respectively represents a         nitrogen atom,

(iii) and a molybdenum source selected from molybdenum trioxide or molybdates, preferably ammonium molybdate.

In one embodiment of the invention, the organomolybdenum compound may comprise from 0.1 to 30% by weight, preferably from 0.1 to 20% by weight, more preferably from 2 to 8.5% by weight of molybdenum compared to the total weight of the organomolybdenum complex.

Preferably, the organomolybdenum compound comprises at least one organic molybdenum complex of formula (I) or (II), alone or in mixture:

-   -   wherein:     -   X¹ represents an oxygen atom or a nitrogen atom;     -   X² represents an oxygen atom or a nitrogen atom;     -   n represents 1 when X¹ represents an oxygen atom and m         represents 1 when X² represents an oxygen atom;     -   n represents 2 when X¹ represents a nitrogen atom and m         represents 2 when X² represents a nitrogen atom;     -   R₁ represents a linear or branched, saturated or unsaturated         alkyl moiety comprising from 4 to 36 carbon atoms, preferably         from 4 to 20 carbon atoms, advantageously from 6 to 18 carbon         atoms;

-   -   wherein:     -   X¹ represents an oxygen atom or a nitrogen atom;     -   X² represents an oxygen atom or a nitrogen atom;     -   n represents 1 when X¹ represents an oxygen atom and m         represents 1 when X² represents an oxygen atom;     -   n represents 2 when X¹ represents a nitrogen atom and m         represents 2 when X² represents a nitrogen atom;     -   R₁ represents a linear or branched, saturated or unsaturated         alkyl moiety comprising from 4 to 36 carbon atoms, preferably         from 4 to 20 carbon atoms, advantageously from 6 to 18 carbon         atoms;     -   R₂ represents a linear or branched, saturated or unsaturated         alkyl moiety comprising from 4 to 36 carbon atoms, preferably         from 4 to 20 carbon atoms, advantageously from 6 to 18 carbon         atoms.

Advantageously, the organic molybdenum complex of formula (I) or (II) is prepared by the reaction of:

-   -   (i) a mono-, di- or tri-glyceride fat or fatty acid,     -   (ii) diethanolamine or 2-(2-aminoethyl) aminoethanol,     -   (iii) and a molybdenum source selected from molybdenum trioxide         or molybdates, preferably ammonium molybdate.

More advantageously, the organic molybdenum complex of formula (I) consists of at least one compound of formula (I-a) or (I-b), alone or as a mixture:

-   -   wherein R₁ represents a linear or branched, saturated or         unsaturated alkyl moiety comprising from 4 to 36 carbon atoms,         preferably from 4 to 20 carbon atoms, advantageously from 6 to         18 carbon atoms;

-   -   wherein R₁ represents a linear or branched, saturated or         unsaturated alkyl moiety comprising from 4 to 36 carbon atoms,         preferably from 4 to 20 carbon atoms, advantageously from 6 to         18 carbon atoms.

An example of a sulphur-free molybdenum complex according to the invention is Molyvan 855® marketed by the company Vanderbilt.

In another embodiment of the invention, the organomolybdenum compound is selected from organic complexes of molybdenum with dithiophosphate ligands or organic complexes of molybdenum with dithiocarbamate ligands.

In the sense of the invention, organic complexes of molybdenum with dithiophosphate ligands are also referred to as molybdenum dithiophosphates or Mo-DTP compounds and organic complexes of molybdenum with dithiocarbamate ligands are also referred to as molybdenum dithiocarbamates or Mo-DTC compounds.

In one more preferred embodiment of the invention, the organomolybdenum compound is selected from molybdenum dithiocarbamate.

Mo-DTC compounds are complexes formed by a molybdenum metal core bound to one or more ligands, the ligand being an alkyl dithiocarbamate moiety. These compounds are well-known to the skilled person.

In one embodiment of the invention, the Mo-DTC compound may comprise from 1 to 40%, preferably from 2 to 30%, more preferably from 3 to 28%, advantageously from 4 to 15% by weight of molybdenum, compared to the total weight of the Mo-DTC compound.

In another embodiment of the invention, the Mo-DTC compound may comprise from 1 to 40%, preferably from 2 to 30%, more preferably from 3 to 28%, advantageously from 4 to 15% by weight of sulphur, compared to the total weight of the Mo-DTC compound.

In a preferred embodiment of the invention, the Mo-DTC compound is a dimeric Mo-DTC compound.

Examples of dimeric Mo-DTC compounds are the compounds and their preparation methods as described in EP 0757093, EP 0719851, EP 0743354 or EP 1013749.

Dimeric Mo-DTC compounds generally correspond to compounds of formula (III):

-   -   wherein:     -   R₃, R₄, R₅, R₆, which may be identical or different,         independently represent a hydrocarbon moiety selected from         alkyl, alkenyl, aryl, cycloalkyl or cycloalkenyl moieties,     -   X₃, X₄, X₅ et X₆, which may be identical or different,         independently represent an oxygen atom or a sulphur moiety.

“Alkyl moiety” within the meaning of the invention means a linear or branched, saturated or unsaturated hydrocarbon moiety comprising from 1 to 24 carbon atoms, preferably from 4 to 18 carbon atoms.

In one embodiment of the invention, the alkyl moiety is selected from the group consisting of methyl, ethyl, propyl, isopropyl, n-butyl, iso-butyl tert-butyl, n-pentyl, iso-pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, isotridecyl, tetradecyl hexadecyl, stearyl, icosyl, docosyl, tetracosyl, triacontyl, 2-ethylhexyl, 2-butyloctyl, 2-butyldecyl, 2-hexyloctyl, 2-hexyldecyl, 2-octyldecyl, 2-hexyldodecyl, 2-octyldodecyl, 2-decyltetradecyl, 2-dodecylhexadecyl, 2-hexadecyloctadecyl, 2-tetradecyloctadecyl, myristyl, palmityl and stearyl.

“Alkenyl moiety” in the sense of the present invention means a linear or branched hydrocarbon moiety comprising at least one double bond and comprising from 2 to 24 carbon atoms. The alkenyl moiety may be selected from vinyl, allyl, propenyl, butenyl, isobutenyl, pentenyl, isopentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tetradecenyl and oleic.

“Aryl moiety” in the sense of the present invention means a polycyclic aromatic hydrocarbon or an aromatic moiety, whether or not substituted by an alkyl moiety. The aryl moiety may comprise from 6 to 24 carbon atoms.

In one embodiment, the aryl moiety may be selected from the group consisting of phenyl, toluyl, xylyl, cumenyl, mesityl, benzyl, phenethyl, styryl, cinnamyl, benzhydryl, trityl, ethylphenyl, propylphenyl butylphenyl, pentylphenyl, hexylphenyl, heptylphenyl, octylphenyl, nonylphenyl, decylphenyl, undecylphenyl, dodecylphenyl, phenylphenyl, benzylphenyl, phenylstyrene, p-cumylphenyl and naphthyl.

“Cycloalkyl moiety” in the sense of the present invention means a polycyclic or cyclic hydrocarbon, whether or not substituted by an alkyl moiety.

“Cycloalkenyl moiety” in the sense of the present invention means a polycyclic or cyclic hydrocarbon, whether or not substituted by an alkyl moiety, and comprises at least one double bond.

Cycloalkyl moieties and cycloalkenyl moieties may comprise from 3 to 24 carbon atoms.

For the purposes of the present invention, cycloalkyl moieties and cycloalkenyl moieties may be selected, without limitation, from the group consisting of cyclopentyl, cyclohexyl, cycloheptyl, methylcyclopentyl, methylcyclohexyl, methylcycloheptyl, cyclopentenyl, cyclohexenyl, cycloheptenyl, methylcyclopentenyl, methylcyclohexenyl.

In one preferred embodiment of the invention, R₃, R₄, R₅ and R₆, which may be the same or different, independently represent an alkyl moiety comprising from 1 to 24 carbon atoms, preferably from 4 to 18 carbon atoms, or an alkenyl moiety comprising from 2 to 24 carbon atoms.

In one embodiment of the invention, X₃, X₄, X₅ and X₆ may be identical and may represent a sulphur atom.

In another embodiment of the invention, X₃, X₄, X₅ and X₆ may be identical and may be an oxygen atom.

In another embodiment of the invention, X₃ and X₄ may represent a sulphur atom and X₅ and X₆ may represent an oxygen atom.

In another embodiment of the invention, X₃ and X₄ may represent an oxygen atom and X₅ and X₆ may represent a sulphur atom.

In another embodiment of the invention, the ratio of the number of sulphur atoms to the number of oxygen atoms (S/O) of the Mo-DTC compound may vary from (1/3) to (3/1).

In another embodiment of the invention, the Mo-DTC compound of formula (III) may be selected from a symmetrical Mo-DTC compound, an asymmetrical Mo-DTC compound and a combination thereof.

“Symmetric Mo-DTC compound” according to the invention means a Mo-DTC compound of formula (V) in which the moieties R₃, R₄, R₅ and R₆ are identical.

“Asymmetric Mo-DTC compound” according to the invention means an Mo-DTC compound of formula (V) in which the moieties R₃ and R₄ are identical, the moieties R₅ and R₆ are identical and the moieties R₃ and R₄ are different from the moieties R₅ and R₆.

In a preferred embodiment of the invention, the Mo-DTC compound is a mixture of at least one symmetric Mo-DTC compound and at least one asymmetric Mo-DTC compound.

In one embodiment of the invention, R₃ and R₄, which are identical, represent an alkyl moiety comprising from 5 to 15 carbon atoms, preferably from 8 to 13 carbon atoms, and R₅ and R₆, which are identical, represent an alkyl moiety comprising from 5 to 15 carbon atoms, preferably from 8 to 13 carbon atoms, and the moieties R₃ and R₄ are identical or different from the moieties R₅ and R₆.

In another preferred embodiment of the invention, R₃ and R₄, which are identical, represent an alkyl moiety comprising from 6 to 10 carbon atoms and R₅ and R₆, which are identical, represent an alkyl moiety comprising from 10 to 15 carbon atoms, and the moieties R₃ and R₄ are different from the moieties R₅ and R₆.

In another preferred embodiment of the invention, R₃ and R₄, which are identical, represent an alkyl moiety comprising from 10 to 15 carbon atoms and R₅ and R₆, which are identical, represent an alkyl moiety comprising from 6 to 10 carbon atoms, and the moieties R₃ and R₄ are different from the moieties R₅ and R₆.

In another preferred embodiment of the invention, R₃, R₄, R₅ and R₆, which are identical, represent an alkyl moiety comprising from 5 to 15 carbon atoms, preferably from 8 to 13 carbon atoms.

Advantageously, the Mo-DTC compound is selected from compounds of formula (III) in which:

-   -   X₃ and X₄ represent an oxygen atom,     -   X₅ and X₆ represent a sulphur atom,     -   R₃ represents an alkyl moiety comprising 8 carbon atoms or an         alkyl moiety comprising 13 carbon atoms,     -   R₄ represents an alkyl moiety comprising 8 carbon atoms or an         alkyl moiety comprising 13 carbon atoms,     -   R₅ represents an alkyl moiety comprising 8 carbon atoms or an         alkyl moiety comprising 13 carbon atoms,     -   R₆ represents an alkyl moiety comprising 8 carbon atoms or an         alkyl moiety comprising 13 carbon atoms.

Thus, advantageously, the Mo-DTC compound is selected from the compounds of formula (III-a)

in which the moieties R₃, R₄, R₅ and R₆ are as defined for formula (III).

More advantageously, the Mo-DTC compound is a mixture:

-   -   of a Mo-DTC compound of formula (III-a) wherein R₃, R₄, R₅ and         R₆ represent an alkyl moiety comprising 8 carbon atoms,     -   of a Mo-DTC compound of formula (III-a) wherein R₃, R₄, R₅ and         R₆ represent an alkyl moiety comprising 13 carbon atoms, and/or     -   of a Mo-DTC compound of formula (III-a) wherein R₃, R₄ represent         an alkyl moiety comprising 8 carbon atoms and R₅ and R₆         represent an alkyl moiety comprising 13 carbon atoms.

Examples of Mo-DTC compounds are Molyvan L®, Molyvan 807® or Molyvan 822® marketed by the R.T. Vanderbilt Company® or the products Sakura-lube 200®, Sakura-lube 165®, Sakura-lube 525® or Sakura-lube 600® marketed by the company Adeka.

Preferably, the lubricant composition according to the invention comprises from 50 ppm to 1,500 ppm by weight of elemental molybdenum, preferably from 100 ppm to 1,000 ppm by weight, compared to the total weight of the lubricant composition.

By “2,5-dimercapto-1,3,4 thiadiazole alkyl (poly)carboxylate compound” is meant, within the meaning of the invention, a compound derived from 2,5-dimercapto-1,3,4 thiadiazole, of which at least one of the thiol moieties is substituted by an alkyl (poly)carboxylate moiety.

By “alkyl (poly)carboxylate moiety” is meant, in the sense of the invention, an alkyl moiety substituted by one or more carboxylate moieties. When substituted with a single carboxylate moiety, it is called an “alkyl carboxylate moiety”. When substituted with at least two carboxylate moieties, it is called an “alkyl polycarboxylate moiety”.

Preferably, only one of the thiol moieties is substituted with an alkyl (poly)carboxylate moiety.

More preferably, the 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound is selected from compounds of the following formula (IV):

-   -   wherein R′ is a linear, branched or cyclic, saturated or         unsaturated C₁-C₃₄ alkyl moiety substituted with at least one         C₁-C₃₄ alkyl carboxylate moiety.

Preferably, the moiety R′ is chosen from C₁-C₃₀, more preferably C₁-C₂₀, even more preferably C₁-C₁₀, and advantageously C₁-C₅alkyl moieties, substituted by at least one C₁-C₃₄ alkyl carboxylate moiety.

More preferably, the moiety R′ is selected from methyl, ethyl, propyl, n-butyl, isobutyl, tert-butyl, n-pentyl, iso-pentyl and neopentyl moieties, substituted by at least one C₁-C₃₄ alkyl carboxylate moiety.

Advantageously, the moiety R′ is an ethyl moiety substituted by at least one C₁-C₃₄ alkyl carboxylate moiety.

Preferably, the alkyl carboxylate moiety is selected from C₁-C₃₀, more preferably C₁-C₂₀, even more preferably C₅-C₁₀ alkyl carboxylate moieties.

The alkyl moiety of the alkyl carboxylate moiety may be linear, branched or cyclic.

Preferably, the alkyl moiety of the alkyl carboxylate moiety is selected from branched alkyl moieties.

The alkyl moiety of the alkyl carboxylate moiety may be saturated or unsaturated.

Preferably, the alkyl moiety of the alkyl carboxylate moiety is saturated.

Advantageously, the alkyl carboxylate moiety is a 2-ethylhexyl carboxylate moiety.

In one embodiment, the moiety R′ is substituted with at least two C₁-C₃₄ alkyl carboxylate moieties.

The alkyl carboxylate moieties may be the same or different.

Preferably, according to this embodiment, the alkyl carboxylate moieties are identical.

More preferably, the alkyl carboxylate moieties are all 2-ethylhexyl carboxylate moieties.

According to a preferred embodiment, the 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound has the following formula (V):

Such compounds are commercially available, e.g. from Vanderbilt under the reference Vanlube® 871 (CAS no. 12610453-53-8).

Advantageously, the organomolybdenum compound and the 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound are present in the additive composition according to the invention in a weight ratio ranging from 1:100 to 100:1, preferably from 1:10 to 10:1, more preferably from 1:5 to 5:1.

Preferably, the lubricant oil composition according to the invention comprises from 0.2% to 1.0% by weight of 2,5-dimercapto-1,3,4-thiadiazole, alkyl (poly)carboxylate compound, preferably from 0.2% to 0.9% by weight, e.g. 0.5% by weight, compared to the total weight of the lubricant composition.

The base oil used in the lubricant compositions according to the invention may be oils of mineral or synthetic origin belonging to groupings I to V according to the classes defined in the API classification (or their equivalents according to the ATIEL classification) (table 1) or mixtures thereof.

TABLE 1 Saturated content Sulphur content Viscosity index (VI) Grouping I  <90%  >0.03% 80 ≤ VI < 120 Mineral oils Grouping II ≥90% ≤0.03% 80 ≤ VI < 120 Hydrocracked oils Grouping III ≥90% ≤0.03% ≥120 Hydro-isomerized oils Grouping IV Polyalphaolefins (PAO) Grouping V Esters and other bases not included in Groupings I to IV

Mineral base oils according to the invention include all types of base oils obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, de-alkalization, solvent dewaxing, hydrotreating, hydrocracking, hydroisomerization and hydrofining.

Mixtures of synthetic and mineral oils can also be used.

The base oils of the lubricant compositions according to the invention may also be chosen from synthetic oils, such as certain esters of carboxylic acids and alcohols, and from polyalphaolefins. Polyalphaolefins used as base oils are for example obtained from monomers with 4 to 32 carbon atoms, for example from octene or decene, and whose viscosity at 100° C. is between 1.5 and 15 mm2·s-1 according to ASTM D445. Their average molar weight is generally between 250 and 3,000 according to ASTM D5296.

Advantageously, the lubricant composition according to the invention comprises at least 50% by weight, preferably at least 60% by weight, more preferably at least 70% by weight, compared to the total weight of the composition.

More particularly advantageously, the lubricant composition according to the invention comprises from 50% to 99.5% by weight of base oils, preferably from 70% to 99.5% by weight of base oils, relative to the total weight of the composition.

Many optional additives can also be present in lubricant compositions according to the invention.

Preferred additives for the lubricant composition according to the invention are selected from detergent additives, friction modifying additives other than the molybdenum compounds defined above, extreme pressure additives, dispersants, pour point depressants, anti-foaming agents, thickeners and mixtures thereof.

Preferably, the lubricant compositions according to the invention comprise at least one extreme pressure additive, or a mixture.

Anti-wear additives and extreme pressure additives protect surface friction by forming a protective film adsorbed on its surfaces.

There are a wide variety of anti-wear additives. Preferably, for the lubricant compositions of the invention, the anti-wear additives are chosen from additives comprising phosphorus and sulphur such as alkylthiophosphate metals, in particular zinc alkylthiophosphate, and more precisely zinc dialkyldithiophosphate or ZnDTP. Preferred compounds are of the formula Zn((SP(S)(OR)(OR′))₂, wherein R and R′, the same or different, independently represent an alkyl moiety, preferably an alkyl moiety comprising from 1 to 18 carbon atoms.

Amine phosphates are also anti-wear additives which can be used in the lubricant compositions according to the invention. However, the phosphorus atoms provided by these additives can act as a poison for automotive catalytic systems as these additives are ash generators. These effects can be minimized by partially substituting amine phosphates with non-phosphorous additives, such as polysulphides, especially sulphur-containing olefins.

Advantageously, the lubricant compositions according to the invention may comprise from 0.01 to 6% by weight, preferably from 0.05 to 4% by weight, more preferably from 0.1 to 2% by weight compared to the total weight of lubricant composition, anti-wear additives and extreme pressure additives.

Advantageously, the lubricant compositions according to the invention comprise from 0.01 to 6% by weight, preferably from 0.05 to 4% by weight, more preferably from 0.1 to 2% by weight compared to the total weight of lubricant composition, of anti-wear additives (or anti-wear compounds).

Advantageously, the compositions according to the invention may comprise at least one friction modifier additive different from the molybdenum compounds of the invention. The friction modifier additives may be selected from compounds providing metallic elements and ash-free compounds. Among the compounds providing metallic elements, we can mention transition metal complexes such as Mo, Sb, Sn, Fe, Cu, Zn, whose ligands can be hydrocarbon compounds comprising oxygen, nitrogen, sulphur or phosphorus atoms. Ash-free friction modifier additives are generally of organic origin or may be selected from fatty acid monoesters of polyols, alkoxylated amines, alkoxylated fatty amines, fatty epoxides, fatty epoxide borates, fatty amines or glycerol acid esters. According to the invention, the fatty compounds comprise at least one hydrocarbon moiety comprising 10 to 24 carbon atoms.

Advantageously, the lubricant composition according to the invention may comprise anti-wear additives and extreme pressure additives in an amount ranging from 0.01 to 2% by weight or 0.01 to 5% by weight, preferably from 0.1 to 1.5% by weight, or from 0.1 to 2% by weight compared to the total weight of lubricant composition.

Advantageously, the lubricant composition according to the invention may comprise at least one antioxidant additive.

Antioxidant additives generally delay the degradation of the lubricant composition. This degradation may result in the formation of deposits, the presence of sludge or an increase in the viscosity of the lubricant composition.

Antioxidant additives act as radical inhibitors or hydroperoxide destroyer inhibitors. Commonly used antioxidants include phenolic antioxidants, amine antioxidants, and sulphur- and phosphorus-containing antioxidants. Some of these antioxidants, for example those containing sulphur and phosphorus, can generate ash. Phenolic antioxidant additives can be ash-free or in the form of neutral or basic metal salts. The antioxidant additives may in particular be selected from sterically hindered phenols, sterically hindered phenol esters and sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylamines substituted by at least one C1-C12 alkyl moiety, N,N′-dialkyl-aryl-diamines and mixtures thereof.

Preferably according to the invention, the sterically hindered phenols are chosen from compounds comprising a phenol moiety in which at least one of the carbon atoms in the vicinity of the carbon atom bearing the alcohol function is substituted by at least one C1-C10 alkyl moiety, preferably a C1-C6 alkyl moiety, preferably a C4 alkyl moiety, preferably by a ter-butyl moiety.

Amino compounds are another class of antioxidant additives that can be used, optionally in combination with phenolic antioxidant additives. Examples of amino compounds are aromatic amines, for example aromatic amines of the formula NRaRbRc where Ra represents an aliphatic moiety or an aromatic moiety, optionally substituted, Rb represents an aromatic moiety, optionally substituted, Rc represents a hydrogen atom, an alkyl moiety, an aryl moiety or a moiety of formula RdS(O)zRe in which Rd represents an alkylene moiety or an alkenylene moiety, Re represents an alkyl moiety, an alkenyl moiety or an aryl moiety and z represents 0, 1 or 2.

Alkyl phenols containing sulphur or their alkali or alkaline earth metal salts can also be used as antioxidant additives.

Other classes of antioxidant additives are compounds comprising copper, e.g. copper thio- or dithio-phosphates, copper salts of carboxylic acids, dithiocarbamates, sulphonates, phenates, copper acetylacetonates. Copper I and II salts, succinic acid or anhydride salts can also be used.

The lubricant compositions according to the invention may also comprise any type of antioxidant known to the person skilled in the art.

Advantageously, the lubricant composition comprises at least one ash-free antioxidant additive.

Equally advantageously, the lubricant composition according to the invention comprises from 0.1 to 2% by weight, compared to the total weight of the composition, of at least one antioxidant additive.

The lubricant composition according to the invention may also comprise at least one detergent additive.

Detergent additives generally reduce the formation of deposits on the surface of metal parts by dissolving oxidation and combustion by-products.

The detergent additives that can be used in the lubricant compositions according to the invention are generally known to the person skilled in the art. Detergent additives can be anionic compounds comprising a long lipophilic hydrocarbon chain and a hydrophobic head. The associated cation may be a metal cation of an alkali or alkaline earth metal.

The detergent additives are preferably selected from alkali or alkaline earth metals of carboxylic acids, sulphonates, salicylates, naphthenates, and phenate salts. The alkali and alkaline earth metals are preferably calcium, magnesium, sodium or barium.

These metal salts generally contain the metal in a stoichiometric amount or in excess, i.e. in an amount greater than the stoichiometric amount. These are overbased detergent additives; the excess metal giving the overbased character to the detergent is generally in the form of oil-insoluble metal salts, e.g. carbonate, hydroxide, oxalate, acetate, glutamate, preferably carbonate.

Advantageously, the lubricant composition according to the invention may comprise from 0.5% to 8% or from 2% to 4% by weight of overbased detergent additives relative to the total weight of the lubricant composition.

Equally advantageously, the lubricant composition according to the invention may also comprise at least one pour point depressant additive.

By slowing down the formation of paraffin crystals, the pour point depressant additive generally improves the cold behavior of the lubricant composition according to the invention.

Examples of pour point depressants are alkyl polymethacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalene, alkyl polystyrenes.

Advantageously, the lubricant composition according to the invention may also comprise a dispersing agent.

The dispersing agents may be selected from Mannich bases, succinimides and derivatives thereof.

Advantageously, the lubricant composition according to the invention may comprise from 0.2% to 10% by weight of dispersant(s) compared to the total weight of the lubricant composition.

Advantageously, the lubricant composition of the present invention may also comprise at least one additional polymer that can improve the viscosity index. Examples of additional viscosity index improving polymers are polymeric esters, hydrogenated or non-hydrogenated homopolymers or copolymers of styrene, butadiene and isoprene, polymethacrylates (PMA). Equally advantageously, the lubricant composition according to the invention may comprise from 1 to 15% by weight, compared to the total weight of the lubricant composition, of an additive improving the viscosity index.

The lubricant composition according to the invention may also comprise at least one thickening agent.

The lubricant composition according to the invention may also comprise an anti-foaming agent and a demulsifier.

Advantageously, the lubricant composition according to the invention comprises:

-   -   from 50% to 99.5% by weight of base oil,     -   from 0.1% to 1.5% by weight of organomolybdenum compound,     -   from 0.2% to 1.0% by weight of 2,5-dimercapto-1,3,4-thiadiazole         alkyl (poly)carboxylate compound,     -   optionally, from 0.1% to 45% by weight of additives,

compared to the total weight of the lubricant composition.

More advantageously, the lubricant composition according to the invention comprises:

-   -   from 60% to 99.5% by weight of base oil,     -   from 0.1% to 1% by weight of organomolybdenum compound,     -   from 0.2% to 0.9% by weight of 2,5-dimercapto-1,3,4-thiadiazole         alkyl (poly)carboxylate compound,     -   optionally, from 0.5% to 40% by weight of additives,

compared to the total weight of the lubricant composition.

Preferably, the lubricant composition has a sulphur content ranging from 0.01% to 5% by weight, preferably from 0.1% to 2% by weight, more preferably from 0.1% to 0.5% by weight, compared to the total weight of the lubricant composition.

The invention also relates to the use of a 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound to protect an organomolybdenum compound, e.g. MoDTC, from degradation, preferably to protect the organomolybdenum compound, e.g. MoDTC, from oxidation.

The present invention also relates to the use of a 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound in a lubricant composition comprising at least one base oil and at least one organomolybdenum compound, e.g. an organic complex of molybdenum with dithiocarbamate ligands, to maintain the fuel economy properties of the lubricant composition over time.

The present invention also relates to a method for protecting from degradation, in particular by oxidation, the organomolybdenum compound, for example MoDTC, of a lubricating composition comprising at least one base oil and an organomolybdenum compound, for example MoDTC, comprising the addition, to said lubricating composition, of a 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound.

The present invention also relates to a method of maintaining over time the fuel economy properties of a lubricating composition comprising at least one base oil and an organomolybdenum compound, e.g. MoDTC, comprising the addition to said lubricating composition of a 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound.

The variants and embodiments detailed below for the organomolybdenum compound and for the 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound also apply to the different uses defined above.

The maintenance of the fuel economy properties of a lubricant composition can typically be assessed by determining the change in the coefficient of friction of the composition during the operation of an engine lubricated with the composition being tested.

During engine operation and at regular time intervals, a sample of the lubricant composition is taken.

The coefficient of friction of the composition is then measured by any method known to the skilled person. This can be done, for example, by means of a reciprocating ball-on-flat tribometer. It is understood that the lower the coefficient of friction over time, the more the effects on the fuel economy properties of the lubricant composition are maintained over time.

Thus, and in a particularly advantageous way, the use of a 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound combined with an organomolybdenum compound, preferably a dinuclear organomolybdenum compound, allows:

-   -   the extension of the properties of the organomolybdenum         compound, e.g. MoDTC, over time, in particular as a lubricant,         preferably as a friction modifier;     -   maintaining the fuel economy properties over time of a lubricant         composition comprising at least one base oil and an         organomolybdenum compound, e.g. MoDTC; and/or     -   maintaining fuel economy over time.

The particular, advantageous or preferred features of the combined use according to the invention define particular, advantageous or preferred combinations usable according to the invention.

EXAMPLES

The compositions detailed below were prepared from the following compounds:

-   -   Base oil: Formulated base oil of grade 0 W-12.

This base oil comprises:

-   -   81.7% by weight of base oil,     -   17.8% by weight of usual additives (4.4% viscosity index         improver, 0.5% oxidizing additive, 0.20% pour point depressant         and 12.7% of an additive package), and     -   0.05% by weight of molybdenum dithiocarbarmate (hereinafter         MoDTC), compared to the total weight of the base oil.     -   the compound 2,5-dimercapto-1,3,4-thiadiazole alkyl         polycarboxylate: compound of formula (V) defined above,         hereinafter Thiadiazole.

Example 1: Preparation of the Compositions

The C0 and C1 compositions are prepared by mixing the different components in the amounts shown in Table 2 below.

Composition C0 is a reference composition (non-additivated base oil).

Composition C1 is a composition according to the invention.

TABLE 2 C0 C1 Base oil (% by weight) 100 99.5 of which Organomolybdenum 0.05 0.05 (% by weight) Thiadiazole — 0.5 (% by weight)

Example 2: Engine Tests

The coefficients of friction of the C0 and C1 lubricant compositions are measured under engine test conditions according to the following method.

Each lubricant composition (10 Kg) is evaluated in a cleanliness test of a turbocharged petrol engine. The engine has a displacement of 1.6 L for 4 cylinders. Its power is 115 kW. The test cycle time is 30 hours, alternating between idle speed (between 500 and 750 rpm) and heavy traffic speed (between 2,500 and 5,800 rpm). The temperature of the lubricant composition shall be between 50 and 150° C. and the temperature of the water in the cooling system shall be between 50 and 97° C. No draining or topping up of the lubricant composition is carried out during the test. E10 fuel is used.

During the test, at T=0 h, 48 h, 72 h, 96 h, 120 h, 144 h and 168 h, a 2-3 mL sample of the lubricant composition is taken and the coefficient of friction of this composition is measured by means of a tribometer with a rotating three-flat ball contact having the following characteristics:

-   -   balls' diameter: 5 mm,     -   temperature: 100° C.,     -   frequency: 5 Hz,     -   maximum contact pressure: 700 MPa     -   trace length: 5 mm     -   duration: 1 h.

The results are shown in Table 3 below and also in FIG. 1 .

TABLE 3 Sampling Friction coefficient time (T) C0 C1  T 0 h 0.035 0.043 T 48 h 0.035 — T 72 h 0.131 0.035 T 96 h 0.136 0.044 T 120 h  — 0.086 T 144 h  — 0.126 T 168 h  0.134 —

These results (Table 3) and the curves in FIG. 1 show that the use of a 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound when present in a lubricant composition comprising an organomolybdenum compound enables the lubricant compositions according to the invention used in an engine test to maintain a low coefficient of friction, in contrast to comparative compositions comprising an organomolybdenum compound alone.

It is therefore demonstrated by means of engine tests simulating the actual conditions of use of the lubricant in an engine that the use of a 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound in a composition comprising an organomolybdenum compound, such as MoDTC, makes it possible to protect the organomolybdenum compound from oxidation over time and consequently to obtain a low coefficient of friction for the lubricating composition over time. It is understood that the lower the coefficient of friction over time, the more the effects on the fuel economy properties of the lubricant composition are maintained over time. 

1. A lubricating oil additive composition comprising: at least one organomolybdenum compound, and at least one 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound.
 2. The additive composition according to claim 1, wherein the organomolybdenum compound is chosen from dinuclear organomolybdenum compounds.
 3. The additive composition according to claim 1, wherein the 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound is selected from compounds of the following formula (IV):

wherein R′ is a C₁-C₃₄ alkyl moiety substituted with at least one C₁-C₃₄ alkyl carboxylate moiety.
 4. The additive composition according to claim 3, wherein R′ is a C₁-C₃₀ alkyl moiety.
 5. The additive composition according to claim 3, wherein the alkyl carboxylate moiety(-ies) are independently chosen from C₁-C₃₀ alkyl carboxylate moieties.
 6. The additive composition according to claim 1, wherein the 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound has the following formula (V):


7. The additive composition according to claim 1, wherein the weight ratio between the organomolybdenum compound and the 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound ranges from 1:100 to 100:1.
 8. A lubricant composition comprising: at least one base oil; and at least one additive composition as defined in claim
 1. 9. The lubricant composition according to claim 8, comprising from 50% to 99.5% by weight of base oil relative to the total weight of the lubricant composition.
 10. The lubricant composition according to claim 9, wherein the content of elemental molybdenum ranges from 50 to 1,500 ppm by weight, compared to the total weight of the lubricant composition.
 11. The lubricant composition according to claim 9, comprising from 0.2% to 1.0% by weight of 2,5-dimercapto-1,3,4-thiadiazole, alkyl (poly)carboxylate compound, compared to the total weight of the lubricant composition.
 12. The lubricant composition according to claim 9, having a sulphur content ranging from 0.01% to 5% by weight, compared to the total weight of the composition.
 13. A method of maintaining over time the fuel economy properties of a lubricating composition comprising at least one base oil and an organomolybdenum compound, said method comprising the addition to said lubricating composition of a 2,5-dimercapto-1,3,4-thiadiazole alkyl (poly)carboxylate compound.
 14. (canceled)
 15. The method according to claim 13, wherein the organomolybdenum compound is chosen from dinuclear organomolybdenum compounds.
 16. The additive composition according to claim 1, wherein the organomolybdenum compound is chosen from molybdenum dithiocarbamates.
 17. The additive composition according to claim 4, wherein R′ is a C1-C20 alkyl moiety.
 18. The additive composition according to claim 17, wherein R′ is a C1-C10 alkyl moiety.
 19. The additive composition according to claim 18, wherein R′ is an ethyl moiety.
 20. The additive composition according to claim 5, wherein the alkyl carboxylate moiety(-ies) are independently chosen from C1-C20 alkyl carboxylate moieties.
 21. The additive composition according to claim 20, wherein the alkyl carboxylate moiety(-ies) are 2-ethylhexyl carboxylate moieties. 